In the film-forming apparatus for forming a thin film according to film-forming techniques such as the sputtering technique, the vacuum evaporation technique, the ion-plating technique, and the CVD technique, a film of a metal or a metal compound constituting a film-forming material is inevitably adhered to the constituent member for the film-forming chamber to be arranged within the film-forming apparatus, during the film-forming process. As such constituent members for the film-forming chamber, there can be listed, for instance, an adhesion-inhibiting plate for avoiding any adhesion of films on the interior of the vacuum vessel other than a substrate, shutters, a mask for forming a film only on a desired area of the substrate, and a tray for transferring substrates. A film having a composition the same as that of an intended thin film (the thin film to be formed on the surface of a substrate) is also deposited on the surface of these members, during the film-forming process. In this respect, it is common that these members are repeatedly used in the film-forming process after the removal of the deposited film.
The thickness of the film inevitably adhered to these constituent members for the foregoing film-forming chamber increases along with the increase in the operating time of the film-forming process. These adhered films may easily be peeled off, in the form of particles, from the constituent members for the film-forming chamber. The formation of these particles of the adhered films is caused by any internal stress generated in the films and/or any stress generated therein due to the repeated heat history and such particles are then adhered to the surface of a substrate. The formation of such particles in turn becomes a cause of various defects of the resulting thin film. For this reason, the constituent members for the film-forming chamber are in general reused in the film-forming process after periodically subjecting them to a series of treatments, which comprises the steps of the removal of the constituent members from the film-forming chamber at such a stage that any adhered film has not yet been peeled off from the surface thereof; the removal of the adhered film through washing the constituent members; and the subsequent surface finishing treatment.
Accordingly, when used as such film-forming materials are, for instance, valuable metals such as Al, Mo, Ti, Cu, Ag, Au, Pt, Rh, Ru, Ir, Ta, W, Nb, Zr, Re, Ni, Cr, V, Li, Co, Pd, Nd, In, and Se, alloys of these metals, and oxides such as ITO, ZnO, PZT and TiO2, there has been desired for the establishment of any processing technique simultaneously serving as a means for the recovery of these metals, which do not take part in the formation of a film on the surface of a substrate, but are adhered to the surface of the constituent member for the film-forming chamber other than the substrate and a means for the reuse of these constituent members.
For instance, in the case of an adhesion-inhibiting plate which is used, in a film-forming apparatus, for avoiding the adhesion of any film-forming material on the inner walls of the film-forming apparatus and on the surface of each constituent member for the film-forming chamber arranged within the film-forming apparatus, other than the substrate, it would presently be common that the constituent members are reused in the film-forming process after the removal of such materials deposited on the members. Currently used as such methods for the removal of the foregoing film-forming materials deposited on the constituent members are, for instance, the sand blasting technique, the wet etching technique which makes use of an acid or an alkali, and the film-removing technique which makes use of the hydrogen embrittlement through the use of, for instance, hydrogen peroxide, as well as the film-removing technique using electrolysis. In this connection, the adhesion-inhibiting plate or the like is not a little damaged due to the dissolution thereof when practicing the treatment for the removal of such deposited materials. Accordingly, such a constituent member is correspondingly limited in its number of reuse. For this reason, there has been desired for the development of a film-removing technique which can reduce the degree of any possible damage of the adhesion-inhibiting plate or the like as low as possible.
Moreover, if the concentration of the films deposited on the constituent members and subsequently removed from the same is low, in the waste generated during the practice of the foregoing sand blasting method or in the waste liquor originated from the chemical treatment using, for instance, an acid or an alkali, the cost required for the recovery of the valuable metals included in the waste or waste liquor becomes high and this in turn makes the recovery procedures unprofitable. In such case, the films removed from the constituent members have presently been regarded as and disposed as waste.
In addition, in the foregoing chemical treatment, it has been desired to reduce the overall quantity of the chemical solutions or liquids to be used in the treatment. This is because, not only the chemical solution or liquid, per se, used therein is quite expensive, but also the cost required for the treatment of such a chemical liquid becomes high. Moreover, the amount of the chemical solution or liquid should substantially be reduced in view of the prevention of any possible environmental pollution. Furthermore, when carrying out a chemical treatment such as one described above, the film-forming material removed from an adhesion-inhibiting plate would be converted into new chemical substances and accordingly, a further additional cost would be required for isolating or recovering only the film-forming material from the deposits removed from the adhesion-inhibiting plate. For this reason, only the film-forming materials have presently been recovered, which can compensate the recovery cost.
In addition to the foregoing methods for the removal of deposited films, there has been known a technique comprising the steps of practicing a film-forming process within a film-forming apparatus equipped with a constituent member covered with an Al-based film which consists of a water-reactive Al-based composite material having such properties that it can undergo a reaction within a water-containing atmosphere so that it can be made soluble in water; removing and separating any film deposited on the constituent member through the reaction and dissolution of the Al-based film; and then recovering, from the deposited film thus removed, the valuable metals included in the film-forming material (see, for instance, Patent Document 1 specified below). This water-reactive Al-based composite material consists of a combination of Al or an Al alloy and at least one member selected from the group consisting of In and Sn, or an alloy of these metal materials.